Biochemistry and Cell Biology Department, Sankara Nethralaya Hospital, Chennai, Tamil Nadu, India.
Diabetes Care. 2010 Sep;33(9):2031-7. doi: 10.2337/dc10-0132. Epub 2010 Jun 14.
Paraoxonase (PON) exhibits esterase activity (PON-AREase) and lactonase activity (PON-HCTLase), which prevent LDL oxidation and detoxify homocysteine thiolactone (HCTL). The role of HCTL and PON-HCTLase as a risk factor for the microvascular complication in diabetic retinopathy at the level of vitreous has not been investigated.
Undiluted vitreous from patients with proliferative diabetic retinopathy (PDR) (n = 13) and macular hole (MH) (n = 8) was used to determine PON-HCTLase and PON-AREase activity spectrophotometrically. HCTL levels were detected by liquid chromatography-tandem mass spectrometry. In vitro studies were done in primary cultures of bovine retinal capillary endothelial cells (BRECs) to determine the dose- and time-dependent effect of HCTL and homocysteine (Hcys) on PON-HCTLase activity, as well as to determine mRNA expression of PON by RT-PCR.
A significant increase in HCTL and PON-HCTLase activity was observed in PDR compared with MH (P = 0.036, P = 0.001), with a significant positive correlation between them (r = 0.77, P = 0.03). The in vitro studies on BRECs showed a dose- and time-dependent increase in the PON-HCTLase activity and mRNA expression of PON2 when exposed to HCTL and Hcys.
This is the first study showing elevated levels of vitreous HCTL and PON-HCTLase activity in PDR. These elevations are probably a protective effect to eliminate HCTL, which mediates endothelial cell dysfunction. Thus, vitreous levels of HCTL and PON activity can be markers of diabetic retinopathy. The bioinformatics analysis reveals that the structure and function of PON that can be modulated by hyperhomocysteinemia in PDR can affect the dual-enzyme activity of PON.
对氧磷酶（PON）具有酯酶活性（PON-AREase）和内酯酶活性（PON-HCTLase），可防止 LDL 氧化并解毒同型半胱氨酸硫内酯（HCTL）。尚未研究 HCTL 和 PON-HCTLase 作为糖尿病性视网膜病变玻璃体微血管并发症危险因素的作用。
使用来自增生性糖尿病性视网膜病变（PDR）（n = 13）和黄斑裂孔（MH）（n = 8）患者的未稀释玻璃体，通过分光光度法测定 PON-HCTLase 和 PON-AREase 活性。通过液相色谱-串联质谱法检测 HCTL 水平。在牛视网膜毛细血管内皮细胞（BRECs）的原代培养物中进行体外研究，以确定 HCTL 和同型半胱氨酸（Hcys）对 PON-HCTLase 活性的剂量和时间依赖性影响，以及通过 RT-PCR 确定 PON 的 mRNA 表达。
与 MH 相比，PDR 中 HCTL 和 PON-HCTLase 活性显著增加（P = 0.036，P = 0.001），两者之间呈显著正相关（r = 0.77，P = 0.03）。对 BRECs 的体外研究表明，当暴露于 HCTL 和 Hcys 时，PON-HCTLase 活性和 PON2 的 mRNA 表达呈剂量和时间依赖性增加。
这是第一项显示 PDR 玻璃体 HCTL 和 PON-HCTLase 活性升高的研究。这些升高可能是消除介导内皮细胞功能障碍的 HCTL 的一种保护作用。因此，玻璃体 HCTL 和 PON 活性水平可以作为糖尿病性视网膜病变的标志物。生物信息学分析表明，在 PDR 中可由高同型半胱氨酸血症调节的 PON 结构和功能可以影响 PON 的双酶活性。
